Test the “Happy Path”
The “happy path” of code or functionality is the primary purpose, the main reason the software exists. If you composed a single sentence to describe what the software does, you would describe the happy path.
Testing the happy path lays the foundation on which the rest of your tests are built. It establishes the context in which all of the variations add further value. In the sense of tests as documentation, it expresses the purpose in an executable form that can capture regressions and evolve with the functionality.
The happy path may require several tests to fully verify depending on the scope of the test. Start with the one or two characteristic purposes for the initial tests. For a unit test, a single test should capture ...